The invention relates generally to digital signal transmission and reception and more particularly to a system and method for multi-coupling digital signals for use in transmission and/or reception, and to a backplane data bus employing such multi-coupled digital signals.
It is frequently a requirement to provide a high speed digital transport mechanism between hardware components which are physically quite close together. An example of this is the requirement for communication between two or more circuit cards connected through a backplane in a shelf.
Such a transport mechanism requires one or more transmitters, a transmission medium, and one or more receivers. A conventional backplane digital transport apparatus features a transmitter on a first card, a circuit track on the backplane, and a receiver on a second card. In another transport mechanism, a multi-coupling backplane communication system features a transmitter on a transmitting card, backplane transmission tracks with proper terminations, and a plurality of coupling tracks, one each connected to a respective receiver on a receiving card. Signals transmitted by the transmitter onto the backplane are coupled both inductively and capacitively onto the coupling tracks.
The speed and volume of communications required between hardware components has been increasing steadily, and currently in most systems including the examples given above it is the transmitter which is limiting the maximum speed attainable. An increase in transmission rate has typically required a transmitter with a proportionately increased rate, which may in some cases entail a substantially increased cost, or may in other cases not be possible at all due to technology limitations. Furthermore, backplane transmission loss is also proportional to transmission rate in an exponential manner. Thus, the maximum transmission rate may also be limited by the distance over the backplane that communications are to occur. It would be desirable to be able to increase capacities and rates without encountering these disadvantages.
It is an object of the invention to obviate or mitigate one or more of the above identified disadvantages.
The invention provides methods and systems for transmitting data over a printed circuit board such as a backplane for example. The printed circuit board has a number of primary tracks each connected to receive a data stream from a respective transmitter which may be located on a card connected to the printed circuit board for example. The data streams are offset in time with respect to one another such that rising edges and falling edges do not coincide with each other in time, The primary tracks are all electromagnetically coupled to a single coupling track at another location on the printed circuit board, and the coupling track is connected to a receiver which may be located on another card for example. The transmitted data streams are all coupled onto the coupling track with each rising edge of any of the data streams resulting in a positive pulse in a coupled signal, and each falling edge of any of the data streams resulting in a negative pulse in the coupled signal. The receiver is capable of detecting all of the pulses, and thus detecting the data received from all of the transmitters. The received data consists of interleaved bits from each of the data streams, due to the offset in the data streams. It is to be understood that conversions at either the transmitting end or the receiving end may be necessary to impart the necessary degree of parallelism, or serialism to the data streams such that they are in the required format for whatever circuitry which uses or generates them.
The received data stream is a serial data stream which is an integral multiple faster than the speed on each of the transmitted data streams. Advantageously, this means that the transmitter can be designed with a rate which is much slower than that of the receiver.